She's a fickle creature, literary fame. While your Eliots and Audens can rest easy in the knowledge that their celebrity is for the ages, some will find her embrace all too brief, being quickly thrown over for a series of newer, younger gallants. In the case of Jeremy Noel-Tod's updated edition of Ian Hamilton's 1994 Oxford Companion, "all too brief" signifies fewer than 20 years – in literary-historical terms, a mere blink of the eye.

The passage of those years has necessitated a change of title, from "20th-Century" to "Modern" poetry. That, and the increase in pagination (Hamilton came in at a little over 600 pages), may make one suspect that we are dealing with the "long" 20th century here. In fact, Noel‑Tod's starting point is 10 years on from Hamilton's: 1910, when Kipling was in his pomp (it was the year he published "If"), Ezra Pound was making it new in London, and a 22-year-old TS Eliot was getting down to work on "The Love Song of J Alfred Prufrock".

The criteria for inclusion of new poets are much as Hamilton outlined them in 1994: poets must be 30 or above (if still living), writing in English, with at least three (as against Hamilton's one) full-length collections to their name. Organisationally, the new volume is a little different: Noel-Tod has removed entries about particular poetic movements and magazines to an appendix, and excised entries on formal innovations and technical matters entirely, so the main text is now a straightforward biographical dictionary of poets. Unlike Hamilton, who commissioned his entries from about 230 contributors, Noel-Tod has provided most of the new ones himself, as well as updating those on poets who were still active at the time of Hamilton's book.

In the introduction Noel-Tod says he has "removed, replaced, or sought to temper entries which seemed more suited in tone to a bar-room dismissal, and even, in some cases, calculated to start a brawl". This seems a shame. For instance, Martin Seymour-Smith's rubbishing of the once-popular poet WW Gibson ("Gibson's work was consistently uninspired and rhythmically flat. Claims that a few war poems are exceptional do not stand up to investigation") has gone.

In essence, however, it remains Hamilton's book, retaining many of the acerbic judgments and off-piste observations that make it such a pleasure, Seymour-Smith's prominent among them. On the one-time poetry editor of the Paris Review, Michael Benedikt: "Many of his poems have struck critics as loose to the point of carelessness." And on John Drinkwater: "One of those poets who may safely be described as quintessentially Georgian … His work, unlike that of Graves, de la Mare, and even (very occasionally) JC Squire, has failed to last … His greatest interest in later life was philately."

The decision to smooth out some of the earlier edition's eccentricities is understandable – somewhat unconventionally, Hamilton included entries on Stephen Crane, the novelist, who died in 1900 and wrote very little poetry; on Lilian Bowes Lyon, the Queen Mother's cousin, who wrote poems about horses and hares; on Oscar Wilde's quondam lover Alfred Douglas; and on Alex Comfort, physician, pacifist, critic and sometime poet, now remembered principally for The Joy of Sex. Perhaps more controversially, Noel-Tod has seen fit to excise the entry on Bob Dylan.

It is interesting to note who now makes the cut for the first time – as Noel-Tod notes, in the first volume women accounted for just 13% of entries. He has set out to redress the balance. Hence Carol Ann Duffy and Jo Shapcott are now joined by the likes of Lavinia Greenlaw, Kathleen Jamie, Kate Clanchy and Sophie Hannah, among many others. Poets who were young entrants last time round – Simon Armitage, Glyn Maxwell, for instance – are given substantial updates. Don Paterson, missing in 1994 and now a central figure in the poetry publishing scene, is here. And, quite rightly, Roger McGough gets his own entry, having been subsumed in the first edition into a brief paragraph on the Liverpool poets ("a part of sociological rather than literary history", was Seymour-Smith's snootily de haut en bas appraisal).

The most dismal difference between the books, inevitably, is the frequency with which that open hyphen in the poets' dates has had to be closed off – Thom Gunn, Mick Imlah, UA Fanthorpe, Michael Donaghy, Peter Porter … the list is long and grim, and it includes Hamilton himself, whose entry is now much expanded from the brief paragraph he allocated himself in 1994. Hamilton hoped then that his book would be serious and useful, as well as pleasurable. On this point, both he and his successor can be reassured. It remains an essential and enjoyable guide to what Noel-Tod refers to as the disorderly garden of English-language poetry.

One final threnodic note, though plenty of the entries he wrote remain, the one on Seymour-Smith himself – poet, critic, biographer, astrologer – is, alas, no more. Oh yes, she's a fickle thing, literary fame.